On 8/1/07, Dan Weston
The moral of the story is that monads are less than meets the eye. You can create them and concatenate them
I mostly sympathise with your rant, but I think you need to be clearer about what exactly is concatenated. In general you can't concatenate Monads. What you *can* concatenate are Kleisli arrows (ie. things of type Monad m => a -> m b). You can also apply Kleisli arrows to Monads, and that's what >>= does. I feel that talking about Monads without Kleisli arrows is like talking about category theory without arrows, or at least sets without functions. In each case, without the latter, the former is more or less useless. Also, I'm having a terminological difficulty that maybe someone can help with: 'Monad' is a type class. So what's 'IO'? Is the correct terminology 'instance' as in 'IO is an instance of Monad'. I consider 'IO' to be 'a monad' as that fits with mathematical terminology. But what about an actual object of type 'IO Int', say? Some people have been loosely calling such an object 'a monad'. That doesn't seem quite right. Maybe it's 'an instance of IO Int', though that's stretching the word 'instance' to meaning two different things. And if an object of type IO Int is in instance of IO Int, is it reasonable to also call it an 'instance of IO', or even 'an instance of Monad'? I'm sure there are proper words for all these things if someone fills me in. -- Dan